1. Field of the Invention
The present disclosure generally relates to image processing and, more particularly, to a white balance control technique used for image data.
2. Description of the Related Art
Generally, an imaging apparatus using an image sensor, such as a digital camera or a digital video camera, includes a white balance control function of adjusting color tones of captured images. Examples of such white balance control include manual white balance control and auto white balance control. In manual white balance control, an image of a white object is previously captured and white balance coefficients are calculated. The calculated white balance coefficients are then applied to the entire screen. In contrast, in auto white balance control, portions deemed to be white are automatically detected from a captured image and white balance coefficients are calculated from average values of the individual color components on the entire screen. The calculated white balance coefficients are then applied to the entire screen.
Hereinafter, conventional auto white balance control will briefly be described. In conventional auto white balance control, a color evaluation value is calculated for each block in captured image data. If the color evaluation value is included in a white detection region, the block is determined to be white. By calculating an integrated value of the pixels in the block determined to be white, a white balance coefficient is calculated.
However, such white balance control has the following problems. In conventional white balance control, since white needs to be detected for an arbitrary light source, the white detection region is widely set in advance. Thus, depending on the type of light source, the color evaluation value of a chromatic color can be included in the white detection region. In this case, since the chromatic color is erroneously detected as white, there are scenes in which desired white balance control cannot be executed. For example, in a scene in which skin-color objects, such as a wooden floor and cardboard boxes under fluorescent light, occupy a large portion of the image data, when white is detected in white balance control, the skin-color chromatic color such as the wooden floor and cardboard boxes can erroneously be detected as white. As a result, an image having a cooler color tone than it actually looks is generated.
Japanese Patent No. 4320998, discusses a method for calculating a new control value. More specifically, when a change is caused between previous conditional information and current conditional information, a previous control value recorded in a recording unit is combined with a control value obtained based on the current conditional information, to calculate a new control value.
However, since the technique discussed in Japanese Patent No. 4320998, requires not only the current conditional information but also the previous conditional information, the control operation cannot be executed only with the current conditional information. Thus, for example, the technique discussed in Japanese Patent No. 4320998, cannot be applied to white balance control executed when a single still image is captured.